Heimdal startup

[Will Regan]

Hi CDR folks,

A new YC startup (Heimdal) launched about a month ago that's hoping to pull cementitious materials and CO2 out of the ocean. Details (below) are sparse, but thought it'd be worth putting on the group's radar, esp those of you who've spent years working on ocean biogeochemistry. 

https://techcrunch.com/2021/08/30/heimdal-pulls-co2-and-cement-making-materials-out-of-seawater-using-renewable-energy/

https://news.ycombinator.com/item?id=28036927

Bears some similarities to chloralkali, as they co-produce H2 and Cl2. Given that they remove carbonates from seawater, it strikes me as the reverse of ocean liming, which is at odds with their claim that this would increase the ocean's carrying capacity for CO2. Any thoughts?

-Will

(long time listener, first time poster)

[Tom Goreau]

There is nothing new here, this is an imitation of the Biorock materials process which we have been doing since 1976.

 

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance

Chief Scientist, Blue Regeneration SL
President, Biorock Technology Inc.

Technical Advisor, Blue Guardians Programme, SIDS DOCK

37 Pleasant Street, Cambridge, MA 02139

gor...@globalcoral.org
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226 (leave message)

 

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

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Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

 

No one can change the past, everybody can change the future

 

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[Michael Tyka]

Yes, it does sound like chloralkali to make alkalinity and then use that alkalinity to precipitate divalent cation salts. 

We can consider these as two independent processes and thus the net CO2 uptake just depends on the relative stoichiometry of a) compared to b) & c)

a) Chloralkali:    2Cl- + 2H₂O → Cl₂(g) + H₂(g) + 2OH-   

b) Precipitation: Ca(2+) + HCO₃-  +  OH-  → CaCO₃ + H₂O

c) Reabsorption: CO₂ + OH- → HCO₃- 

Adding b) and c) makes it clear that 2 OH- are required to remove a CaCO₃ from the ocean without changing the pH of the ocean: 

Ca(2+) + CO₂(g) + 2OH- → CaCO₃(s) + H₂O

In other words, for every mol of Cl₂ you can create one mole of CaCO3, pull out one mol of CO2 out of the atmosphere and leave the ocean unchanged.

However they don't say what they intend to do with the chlorine. I don't believe there is a gigatonne market for chlorine out there.. ?

If you recombine CL2 and H2 to HCl, you basically have House's method but then you have the hydrochloric acid to contend with (which can't go back in the ocean!)

I'm a little surprised CaCO3 produced this way would be competitive with the typically mined CaCO3? If you're only after the negative emissions then it's

(almost) twice as efficient to just add the OH- to the ocean and absorb CO2 as HCO3 in the ocean, as widely proposed; approximately: 2CO₂ + 2OH- → 2HCO₃- 

M

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[Ken Caldeira]

Thank you, Michael, for this clarity.

One can think of the CO2 disposal problem as an acid disposal problem.

It seems this process is effectively converting a weak acid (H2CO3) into a strong acid (HCl), but we still have the problem of HCl disposal.

You can make H2 and Cl2, but it is hard to see how that is not going to eventually add more HCl to the environment.

a) Chloralkali:    2Cl- + 2H₂O → Cl₂(g) + H₂(g) + 2OH-   

b) Precipitation: Ca(2+) + HCO₃-  +  OH-  → CaCO₃ + H₂O

c) Reabsorption: CO₂ + OH- → HCO₃- 

net)     2Cl- +  2Ca(2+) + 2CO₂ + 2OH-   → Cl₂(g) + H₂(g) + 2CaCO₃ 

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[Nima Keivan]

There's a similar process outlined here in quite a bit of detail. Anode coatings, such as those described here, are proposed as a way of mitigating Chlorine gas production during electrolysis of seawater. 

[Michael Tyka]

Unfortunately going from chlorine to oxygen doesn't solve the problem:

Electrolysis with chlorine evolution:    2Cl- + 2H₂O → Cl₂(g) + H₂(g) + 2OH-   

Electrolysis with oxygen evolution:                 2H₂O → O₂(g) + 2H₂(g)  

As you can see, in the oxygen evolution case no net alkalinity is produced, so it cannot be used to precipitate CaCO₃ 

from the ocean in a net CO2 negative way as you end up removing alkalinity from the ocean. 

Like Ken said, CO2 disposal and acid disposal can be thought of as fungible. 

As far as I can see (and please someone correct me if I misunderstood it) the paper you mention as well as others like it (e.g. 

this one) are not fully stoichiometrically balanced. Either no net alkalinity is being made in which case CaCO₃ precipitation will lead to 

acidification of the ocean and subsequent CO₂ degassing, or they don't consider what to do with all the acid produced (it will need to meet some alkaline rock somewhere).

M

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[steve.rackley]

"Cheap acidity" has been a by-product of the oxidation of fossil carbon. In essence, what we need now is "cheap alkalinity".

One option with low carbon intensity is Harvey's 2008 proposal to disperse limestone particles in upwelling regions. Is anyone aware whether this is being actively worked?

[Greg Rau]

To be clear there is at least some acid produced in the chloralkali process because some of the Cl2 will hydrate in the electrolyte:

Cl2 + H2O --->  HOCl + HCl.  However, to really consume Cl2 at scale you need to make something like PVC or use it as an oxidant in a fuel cell (a la House et al 2007): H2 + Cl2 ---> 2HCl + electricity. House et al proposed neutralizing the HCl with silicate rocks to make neutral and presumably benign Mg/Ca chloride salts.

Water electrolysis using a non-chloride salt as an electrolyte also produces an acid and base, but unless these are separated they recombine in the cell to reform the salt: Na2SO4aq + 3H2O + electricity ---> 2NaOH + H2SO4 + H2 + 0.5O2; 2NaOH + H2SO4 ---> Na2SO4aq + 2H2O.  However, using membranes or in situ neutralization of the acid with silicate (or carbonate) minerals can allow net acid and base production or internal consumption of the acid to allow net production of hydroxide (e.g. NaOH) for air capture. Details here and here.

So if we have a massive sink for acid in the form of alkaline rocks, why is acid consumption from saline, electrolytic production of hydroxide for CDR a showstopper?

As for actual CDR, why make solid carbonate with hydroxide (Heimdal?) when making dissolved bicarbonate is about twice as effective per unit of alkalinity added to SW (plus you are stripping Ca++ from seawater and thus reducing CaCO3 saturation (think of the corals) in the former)?:

Heimdal? 2NaOH + SW Ca(HCO3)2aq  + CO2 ---> CaCO3s + 2NaHCO3aq + H2O (= a little less than 0.5 mol of CDR per mol of NaOH because you are also making some Na2CO3aq. Note that if they are making pure Na2CO3 as one figure indicates, they are doing zero CDR)

vs

me and others; to SW add  2NaOH + 2CO2  (@pH<9)----> 2NaHCO3aq (= a little less than 1 mol CDR per mol NaOH because some Na2CO3aq is also formed, and which actually increases CaCO3 saturation state and coral health (Caldeira et al)).  😉

Greg 

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Greg H. Rau, Ph.D.

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https://www.researchgate.net/profile/Greg_Rau
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Co-founder and CTO, Planetary Hydrogen, Inc.
510 582 5578

[Ken Caldeira]

Greg,

Don't you need to bind the Cl2 in a long-lived product or use it to weather rocks and ger more alkalinity, else it will eventually make its way back to the surface ocean where it will drive CO2 into the atmosphere?

"Eventually" might be a long time and temporary storage has value. A good question is:  

If I pour some dilute HCl solution on average land, what fraction of that acidity will be neutralized by increased silicate weathering (and how much carbonate weathering) and what fraction of that acidity will eventually make it to the sea (and how long will that take)?

Are there any papers addressing that question?

Best,

Ken

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[Greg Rau]

As I said you can bind the Cl2 in a long live product eg, by making a solid like PVC (also good for storing C, esp if from air) or by making HCl that can be converted to long lived metal chlorides via reaction will silicate rock:

Mg2SiO4 +4HCl ----> 2MgCl2 + SiO2 + 2H2O.     

An analogous reaction happens with H2SO4 produced via the Na2SO4+H2O electro splitting that I diagrammed.

Don't remember anyone avocating pouring acid on land though that might work in some regions (land locked basins).  Ceratinly we want to keep acid out of the ocean.  I think the prefered way for rock neturaliztion would be in more controled setings like vats, pools or pouring the acid on heaps of rock (mine tailings) with impervious catchment underneath. The resulting salt could be harvested and stored (somewhere), used or put in the ocean, trace metals permitting (House et al.)   Lets find out the best ways.  The negative-emissions SiO2 formed could have some important uses, eg to reduce the CO2 intensity of builiding materials and electronics. No?

Greg

[Michael Tyka]

Greg,

> So if we have a massive sink for acid in the form of alkaline rocks, why is acid consumption from saline, electrolytic production of hydroxide for CDR a showstopper? 

Oh, sorry, I didn't mean to imply it's a showstopper at all -  quite the opposite, I believe accessing the alkalinity in rocks directly or indirectly via acid neutralization is key. 

I've just recently seen quite a few electrochemical papers that don't seem to mention anything about what happens with the acidity.

The idea of making PVC is very interesting, it's quite stable and inert after all, one could just stack it up somewhere. Are there papers describing this as a strategy ?

The monomer (VCM) though is a gas and quite toxic/carcinogenic and the acid needs to be anhydrous during the synthesis process. 

Makes me shudder to think of scaling up the PVC industry to that scale.. environmentally probably not a good idea ? I think I prefer rocks.. 

> As for actual CDR, why make solid carbonate with hydroxide (Heimdal?) when making dissolved bicarbonate is about twice as effective per unit of alkalinity

Oh yes, I couldn't agree more. If alkalinity is made, it's best to just add it to the ocean. Yet somehow the idea of storing C in CaCO3 appears perennially attractive...

Best,

  Mike

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[John Crusius]

All

PVC is really a horrible product w/ many impacts of its manufacture and use.  You can read about some of that here.

https://healthybuilding.net/blog/475-the-high-cost-of-cheap-pvc

There are many who recommend replacing it with something else, for every existing use.

It would not be a good way to store Cl or C.  I am not super close to this research, but my brother-in-law used to be.

John

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[Andrew Lockley]

Ronning seemingly suggests that this is not a viable strategy, in the paper: Alkaline minerals as a tool to mitigate ocean acidification and facilitate CO2 from the atmosphere

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[Chris Van Arsdale]

I don't suppose you know where one could find a recording of that talk... All I could find was this one slide:

https://presentations.copernicus.org/EGU21/EGU21-2264_presentation.png

I would (very naively) assume the problem stems from the limestone creating new nucleation sites, and calcium carbonate is supersaturated in the most surface ocean... It could crash out, drop below the mix layer, and the 100 day mark would see a reduction in pH?

If so, it might not matter for the Harvey proposal. An upwelling site will (eventually, next 50 years) return most of the alkalinity back to the surface (even if you see a large drop over the 100 day period). Or one could just dump below the mix layer. Unfortunately, the location of said upwelling sites are not exactly convenient, and transport of Gts of limestone is going to be fairly expensive.

- Chris

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[Andrew Lockley]

Ronning discussed this in depth on the Reviewer 2 Does Geoengineering podcast

https://open.spotify.com/episode/5oZnfXVREfnk8G3imTCqbT?si=WLdBCYTcQG2kEQ8rBuxOWg&utm_source=copy-link&dl_branch=1 

[Greg Rau]

John, Thanks for the heads up. I don't want to belabor this or get too far afield, but my point is don't ignore making long lasting polymers if you want useful, long-term storage of C (and Cl2). OK, current PVC production is nasty, so let's clean it up or make some other long lasting, beneficial green polymer.

The precurosr to PVC is ethylene.  Ethylene can be made from ethanol which can be made from the fermentation of biomass:

air CO2 ---> biomass--->fermentation ----> ethanol

Then ethanol can reportedly be converted to ethylene

C2H5OH ---> chemistry--->H2C=CH2

This then can be made into vinyl choride:

2H2C=CH2+ Cl2-----> 2H2CCH2Cl

Then:

H2CCH2Cl + polymerization ---> PVC.

If you run out fo biomass you can abiotically make ethylene (and thus PVC) from air CO2:

air CO2 ---DAC---> conc CO2 + chemistry-----> ethylene

I'm not saying green PVC is the perfect C storage medium, but then neither are trees or soils, plus you can't use the latter for plumbing, electrical cable insulation, imitation leather, flooring, signage, and phonograph records (45 million tonnes/yr = 100 million tonnes of air CO2 storage potential/yr).  Let's eval our options and not throw out any without good reason.

Greg